ATP,ADP and AMP dephosphorylation in membrane fractions of <Emphasis Type="Italic">Rhamdia quelen</Emphasis> exposed to different temperatures

The silver catfish Rhamdia quelen is a teleost species from South America that can resist cold winters and grow quickly in the summer, representing an important species for aquaculture in both temperate and subtropical climates. NTPDase and 5′-nucleotidase are enzymes responsible for the sequence of ATP dephosphorylation to adenosine in a variety of organs. This enzymatic cascade permits the resultant adenosine to be taken up by the cells. In the present study, membrane fractions of brain, liver and kidney from fish Rhamdia quelen exposed to 15, 23 and 31 °C for 21 days (chronic) or 12 h (acute) were incubated with ATP, ADP and AMP as substrates. In the 21 day experiment the results showed that ATP hydrolysis was enhanced by the increase in temperature in all tissues, except for 31 °C in the brain. NTPDase hydrolysis using ADP as substrate showed a behavior similar to that observed for ATP hydrolysis, except for 31 °C, when the behavior was similar to that observed at 15 °C in the brain. 5′-Nucleotidase activity using AMP as substrate raised with increasing temperature in the three tissues studied. In the 12 h experiment the results obtained for the three temperatures did not differ significantly from each other for any of the tissues. We conclude that after a period of 21 days temperature may affect the activity of NTPDase and 5′-nucleotidase, important enzymes implicated in nucleotide degradation.